Device for synchronizing the frequency of an oscillator to a control oscillation



c. E. G. BAILEY 1952 DEVICE FOR SYNCHRONIZING THE FREQUENCY OF 2582668AN OSCILLATOR TO A CONTROL OSCILLATION Filed March 23, 1949 i AWE/V706Patented Jan. 15, 1952 DEVICE FOR SYNCHRONIZING THE FRE- QUENCY OF ANOSCILLATOR TO A CON- TROL OSCILLATION Christopher Edmund Gervase Bailey,London, England, assignor to Hartford National Bank and Trust Company,Hartford, Conn., as trustee Application March 23, 1949, Serial No.83,016 In Great Britain March 10, 1948 Claims.

The inventionflrelates to a device for. synchronizing the frequency ofan oscillator to a control oscillation, more particularly forsynchronizing the frequency of a transmitter to the frequency ofa'standard transmitter, a controlvoltage being produced which, through afrequency corrector, controls the frequency of the oscillator.

Such devices are of utility, for example in systems of transmitters ofthe kind say of Gleichwellen systems and transmitter networks forfrequency-modulated transmitters.

The device according to the invention is distinguished by the featurethat the control-voltage is taken from a phase-discriminator to whichthe output voltages of an amplitude demodulator and a frequencydemodulator are supplied, these two demodulators having supplied to themnot only the oscillation produced by the oscillator but alsotheoscillation modulated by a pilot signal.

In order that the invention may be more clearly understood and readilycarried into effect, it will now be described more fully with referenceto .the accompanying drawing.

Fig. 1 shows a diagrammatic view of a device according to the invention,the operation of which will be set out more fully with reference toFigs. 2 to 7.

Fig. 8 shows, in block diagram form, an alternative embodiment of' thedevice according to the invention.

According to Fig. 1, signals l of a standard transmitter and signals IDfrom an extension transmitter are received with the use of an aerial 2.

From economical considerations it will usually bepreferred to arrangethe aerial 2 in the proximity of the extension transmitter. If such isthe case, the strength of signal I!) may be materially higher than thatof signal I. In order that in this case the receiver 3, which isconnected to the aerial 2, may not be overloaded, it is advantageousto'reduce the ratio in strength of these two signals, for example bygiving a directional characteristic to the aerial 2.

The receiver 3 may be either of the straight or of thesuperheterodynetype. In either case the vector representing thehigh-frequency or intermediate-frequency output voltage of the receiverwill consist (as shown in Fig. 2) of the sum of the vector CA from theextension transmitter and of the vector AB from the standardtransmitter. Assuming the sum vector OB to be at right angles to thevector AB, it is obvious that if the vector AB is phase-modulated by apilot signal, so that this vector takes up positions lying between theextreme positions AB1 and ABz', the resultant is amplitude-modulatedbetween the extreme values DB1 and 032 with thefrequency of the pilotsignal and phase-modulation with this frequency does not take place. Ifthe angle ABO is slightly smaller than theresultant as may be seen fromFig. 3, will exhibit not only amplitude-modulationof the same polarityas before but also phase-modulation, the polarity of which is determinedby the fact that 0131 is situated to the left of 0132. However, if angleABO is slightly larger than 90 (as shown in Fig. 4) the resultant willagain exhibitamplitude-modulation of the same polarity but now togetherwith phase-modulation of opposite polarity, since 0B1 is now situated tothe right of DB2.

The output signal of the receiver 3, which signal corresponds to thevariation between 031 and 0132, is then supplied both to an amplitudedemodulator 4 (Fig. l) and to a frequency de modulator 5. The outputvoltage of the frequency demodulator 5 is. consequently,-zero if AB isat right angles to OB and reverses its polarity when AB turns throughthis position with respect to 0B. The output voltage of the amplitudedemodulator 4 is constant polarity.

The output voltages of the demodulators 4 and 5 with pilot signalfrequency are supplied, preferably through filters cutting oifcomponents with different frequencies, to a phase discriminator 6, whichmay be =constructed,'for example, in the form of a ring demodulator. Theoutput voltage of the phase discriminator 5 will thus be constituted bya direct voltage, the polarity of which reverses simultaneously with thereversal of the polarity of the output voltage of the frequencydemodulator 5. This control-voltage occurring across the output of thephase discriminator is then supplied to a control-device l, whichcorrects the frequency of an extension transmitter 8. The signal In ofthe extension transmitter 8 is emitted by an aerial 9.

If the frequency of the pilot signal is chosen to'be higher than thehighest intelligence-modulation frequency to be transmitted and iftheoutput circuits of the demodulators 4 and 5 and the input circuit ofthe phase discriminator 6 have connected between them filters whichallow the passage of signals of pilot frequency only, the

frequency corrector 1, which is preferably constructed as a reactancetube, may be used in addition for controlling the instantaneousfrequency of the extension transmitter 8 in accordreference numerals'lto 10 designating, parts corresponding to those of the device shown inFig. 1. of the demodulators 4 and 5 and the input circuit of the phasediscriminator B are bandpass filters l2 and I3, respectively, whichallow the passage of the pilot frequencyonly and does not allow thepassage of the frequencies of the intelligence signals. A lowv-passfilter 14, connected between the phase discriminator 6 and the frequencycorrector I, allowsthe passage of. direct voltage and frequencies lower'than of intelligence signals, whereas the band-pass filter l Iconnected between theputput of the amplitude demodulator 4 andthe'frequency corrector 1 allows .the passage of signals withintelligence frequency but not of pilot frequency'or'of direct voltage.In this device the pilot'frequency is. notirestricted to a valueexceeding that of the intelligence 'signals'but instead may be chosen to.be lowerthan or equal to one of these'frequencies.

-The output voltage ofthe phase discriminator Connected between theoutput circuits" 6V controls the central frequency of the extensiontransmitter' in the manner described with reference toIEig. 1, sothatthis central frequency corresponds 'to the central frequency of thestandard transmitter. The variation in the frequencyof. the standardtransmitter due tothe frequency modulation with the intelligencesignalsproduces an output voltage of the amplitude demodulator 4, which,fed to the frequency corrector. 1,. controls the instantaneous.frequency of V the extension transmitter 8. Since a direct voltagecomponent is not passed by the filter l I, there is'. -not..thediliiculty that theioutputvoltage"varies owingsto variations in thedirectional :characteristic curve of the aerial 2 or in'theamplification factor of the receiver 3.

As shown in Figs. 5, 6 and '7, the'device'm'ay also .be .used,.if theamplitude of the controloscillation from the standard transmitter ismodulated by the pilot signal. In this case. the vectorAB. isamplitude-modulated between the values A31 and AB;:. The resultant isconsequently, phase-modulated between the positions 0131 and 0132.If'the angle ABO is'right, CH1 and 032 are equal, so thatamplitude'modulation does not occur. 'If the angle ABO is smallerthani90 '(Eig. 6)., 0B2 exceeds 031 in length and if.- the saidangleexceeds 90(Fig. 7); 031 is the larger of .the two vectors. Theoutputsignal with pilot frequency thus consistsof phase mod- .ulationwith constant polarity and amplitudemodulation the polarity of'whichreverses and becomes zero when the two signals form .a right angle.

' What I claim is:

ply said first and second components to said discriminator to produce acontrol voltage, and means to control the frequency of said generator inaccordance with said control voltage.

2.'Apparatus for synchronizing the? frequency of an oscillationgenerator with standard oscillations modulated by a pilot signalcomprising means to combine the generated oscillations with :thestandard oscillations to produce a resultant wave, a frequency :detectorcoupled to said combinin means, a first filter coupled to the out--plitude detector to extract a second pilot signal component therefrom,

a phase discriminator coupled to the outputs of said first and secondfilters to produce a control voltage depending on thephase difference.between said components, andmeans to control the frequency ofsaidgenerator in accordance with said control voltage.

'3. Apparatus for synchronizing the frequency of an oscillationgenerator with standard oscillations phase modulated by a pilot signalcomprising receiving means to combine the generated oscillations withthe standard oscillations .to-produce a resultant wave,.afrequency-demodulator coupled to said receiving means, a first filtercoupled to the output of said frequency-demodulator to derive therefroma first pilot signal component, an amplitude-demodulator coupled to saidreceiving means, a second filter coupled to the-output of saidamplitudeedemodulator to extract asec- 1. Apparatus for synchronizing'the'frequency wave, means to frequency-demodulate the resultant waveand to extract solely a first pilot signal component. therefrom, meansto amplitude-.demodulate' the resultant wave and to extract solely. asecond pilot signalv component therefrom, a phase discriminator, meansto apond pilot signal component therefrom, a phase discriminatorcoupled. to the outputs of said first and second'filters to produce acontrol voltage dependingon the phase difference between saidcomponents, and means including .a reactance tube tocontrol. thefrequency of saidgenerator in accordance with saidcontrol voltage.

l. "Apparatus .for synchronizing. the frequency of an oscillationgenerator. with standard oscillations amplitude modulatedby a pilotsignal comprising'receiving means to combine the generated oscillationswith the standard oscillations toproduce a resultant wave, afrequency-demodulator coupled to said receiving means, a first filtercoupled to the output of said frequencydemodulator to derive therefrom afirst pilot signal component, an amplitude-demodulator coupled to saidreceiving means, a second filter coupled to the output of saidamplitude-demodulator to extract a second pilot signal componenttherefrom, a. phase discriminator coupled to the outputs of said firstand second filters to produce a control voltage depending on thejphasedifference between said components, and means including a reactance tubeto control the frequency of said generator in accordance with saidcontrol voltage.

5. Apparatusfor synchronizing the frequency of an oscillation generatorwith that of standard oscillations modulated by a pilot signalandfrequency-modulated by an intelligence signal, the frequency of'thepilot signal being higher than the highest frequency in saidintelligence signal, said apparatus comprisingfreceiving means tocombine the generated oscillations with the standard oscillations toproduce a resultant wave, a frequency detector coupled to the output ofthe r'eceiving'means, a firstfilter coupled to the outputof saidfrequency detector to extract solely a first pilot signal componenttherefrom, an amplitude. detector coupled to the. output of saidreceiving means, a second filter coupled to 'the out aceigoea put of,the amplitude modulator to extract solely a second pilot signaltherefrom, a phase discrimi-' nator, means to apply said first andsecond components to said discriminator to produce a con trol voltage, areactance tube coupled to said generator to control the frequencythereof in accord ance lwith an applied voltage, means to apply saidcontrol voltage to said reactance tube to efiect correction of thefrequency of said genera tor,; a,ythird filter coupled to the output ofsaid ampl'tude detector to derive solely the intelli gencei'signalcomponent therefrom, and means to, apply said intelligence signalcomponent to said. reactance tube to modulate the frequency of said-1;

generator accordingly.

15 CHRISTOPHER EDMUND GERVASE BAILEY.

6 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,028,880 Runge et a1 Jan. 28,1936 2,114,036 Smith et a1 Apr. 12, 1938 2,173,902 Gerth et a1 Sept. 26,1939 2,377,326 Crosby June 5, 1945 2,462,857 Ginzton et al. Mar. 1, 1949

